The present invention relates to a locking device for securing the output shaft of an electric tool when the shaft is used manually with electric power.
A conventional electric tool is generally driven by electric power which can be a rechargeable pack or a power supply coming from the wall. An active gear connected to the driving shaft of motor is engaged with a gear set which is then engaged with a passive gear connected to the output shaft. When the electric power is out, the user may use the output shaft manually and the passive gear is used as an active gear to drive the driving shaft of the motor. This causes the drill spins together with the operation and cannot output a torque to unscrew a screw or bolt. Some manufacturers develop a locking device for secure the output shaft during manual operation so that the output shaft can output a torque. The locking device includes several brake pads each having a longitudinal protrusion and a radial protrusion. These brake pads are supposed to contact an inside of a casing in which the output shaft is located. A cam is mounted to the output shaft and rotated with the output shaft. A driving disk is connected to the gear set and includes several fan-shaped bosses which are respectively located between the brake pads. When the driving disk is rotated, the bosses shift the longitudinal protrusions to release the brake status of the brake pads so that the output shaft, the cam and the brake pads are co-rotated. When the driving disk stops, and the output shaft is rotated in opposite direction, the cam pushes the brake pads to contact the inside of the casing to secure the output shaft. However, the longitudinal protrusions of the brake pads could separate from the driving disk when-the driving disk reduces its speed. The brake pads will impact the inside of the casing and generate noise.
In accordance with one aspect of the present invention, there is provided a locking device for output shaft of electric tools and the device includes a casing having a passage through which a shaft extends. The shaft has a polygonal distal end on which a cam is mounted. The cam has a plurality of protrusions and recesses are defined between the protrusions. A plurality of brake pads each have two blocks and are located in the passage of the casing. A driving disk has a plurality of pawls on a first surface thereof and a width of each of the pawls is less than a distance between two blocks of each of the brake pads. A hole is defined through the driving disk and the distal end of the output shaft is engaged with the hole of the driving disk. Two opposite sides of the hole of the driving disk have a hill portion at an intermediate portion thereof. A plurality of concavities are defined in a second surface of the driving disk and each of which receives a spring a ball therein. A cover plate is mounted to the second surface of the driving disk and a plurality of holes are defined through the cover plate. The number of the holes in the cover plate are two times of the number of the concavities in the driving disk. The balls are engaged with half number of the holes. The cover plate has an aperture and two opposite sides of the aperture are in alignment with two opposite sides of the hole in the driving disk.
The primary object of the present invention is to provide a locking device wherein the swing of the brake pads are limited when the rotation of speed of the driving disk is reduced so that the brake pads will not impact the inside of the passage of the casing.
The present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, a preferred embodiment in accordance with the present invention.